1. Field of the Invention
The present invention relates to a joint construction of cobalt-based alloy. More particularly, it relates to a joint construction of cobalt-based alloy, which is well suited when it is applied to a valve and a rotating apparatus having a mechanical seal.
2. Description of the Related Art
As a technology for joining metals of the same kind or metals of different kinds, there are generally known a method in which a brazing filler metal is inserted between an anticorrosion and wear resisting alloy and a base metal to which the alloy is to be joined and only the brazing filler metal is melted and solidified, by which the alloy is joined to the base metal (brazing), a method in which a molten metal is supplied to a joint portion and a base metal to be joined is also melted, by which a layer in which the supplied metal and the base metal are both melted in the joint portion is formed (welding), and a method in which a very thin surface layer of a base metal is melted and a molten metal is deposited on the surface layer, by which the deposited metal is joined to the base metal (build-up).
Also, “Section 3.4.3 Diffusion Welding” in JSME Mechanical Engineers' Handbook, 1987 ed., B2-pp. 63-64 describes diffusion welding in which smooth surfaces of two metallic materials to be joined are brought into contact with each other, and the two metallic materials are joined to each other by a creep phenomenon (caused by the application of a high load) at the contact portion and sintering caused by high temperature in the state in which the metallic materials are maintained at a high temperature. Also, the aforementioned JSME Mechanical Engineers' Handbook describes, as one kind of diffusion welding, a joining method for joining different metals together that does not produce a joint interface, wherein an insert metal containing Ni is inserted between two metallic materials to be joined, and the metallic materials are joined to each other by applying a high load while the metallic materials are maintained at a high temperature. The insert metal is entirely diffused into the two metallic materials to be joined.
Japanese Patent Laid-Open No. 2000-273573 describes a method in which a Co-based, Ni-based, or Fe-based anticorrosion and wear resisting alloy having globular or granular eutectic carbide is joined to a base metal by brazing, welding, or diffusion welding.
The method of joining an anticorrosion and wear resisting alloy to a base metal, which is described in Japanese Patent Laid-Open No. 2000-273573, has problems described below.
In the method in which an anticorrosion and wear resisting alloy is joined to a base metal by melting a brazing filler metal, the metal joining force is weak, so that the joint portion comes off when the temperature increases again to the brazing temperature. According to other methods (welding or diffusion welding), since the metals to be joined are made in a molten state, the globular or granular eutectic carbide of the anticorrosion and wear resisting alloy changes to linear or net-form eutectic carbide. As a result, the characteristics obtained by the globular or granular eutectic carbide are lost. In diffusion welding, since a high load is applied to the metals to be joined at a high temperature at which a creep phenomenon takes place, a high residual stress is created, or a crack develops. Therefore, diffusion welding is unsuitable as a method in which a Co-based anticorrosion and wear resisting alloy having globular or granular eutectic carbide is joined to a base metal while the form thereof is maintained.